Officials from the Food and Drug Administration and the U.S. Department of Agriculture said about 6,000 pigs may have eaten food contaminated with harmful industrial chemicals.

The food went to eight producers in California, Utah, Kansas, New York, Oklahoma, South Carolina and North Carolina, officials said in a teleconference from Washington, D.C. Tainted pet food also made its way to a chicken farm in Missouri.

They said the hogs have been quarantined and that none of the meat would be approved for commercial slaughter.

The rice protein in the food, as well as wheat gluten in other recalled pet foods, was contaminated with melamine and another chemical, cyanuric acid.

Scientists are befuddled about what exactly killed scores of pets in the North America and South Africa. And although the numbers of dead animals has dramatically slowed, veterinarians are still seeing cases.